It is currently Sun Jan 20, 2019 11:51 am

All times are UTC - 7 hours





Post new topic Reply to topic  [ 6 posts ] 
Author Message
PostPosted: Thu Dec 08, 2011 4:28 pm 
Offline

Joined: Wed May 19, 2010 6:12 pm
Posts: 2789
Were there ever any off-the-shelves VDP/PPU chips?

Another question. Why do the NES, SNES, SMS and Genesis all share virtually the same VDP/PPU timing? Did Sega just like how Nintendo did it, or vice versa? Did both base their VDP/PPUs off the same chip series?


Top
 Profile  
 
 Post subject:
PostPosted: Thu Dec 08, 2011 5:47 pm 
Offline

Joined: Sun Sep 19, 2004 11:12 pm
Posts: 21004
Location: NE Indiana, USA (NTSC)
An off-the-shelf Texas Instruments VDP was used in the ColecoVision and MSX. The SMS VDP is a direct descendant of the TMS9918 family, as is the Genesis VDP. The other direct descendant is the VDP in the MSX2 computers. The NES PPU design was inspired by the TMS9918 family because of the ColecoVision's demonstrated ability to show near arcade-perfect Donkey Kong graphics. This includes the tiled background, a sprite unit with fewer sprite shifters than OAM entries (the "secondary OAM"), and the bit about 1 pixel = 2/3 of an NTSC subcarrier period. (Square pixels would have been 7/12.)


Last edited by tepples on Thu Dec 08, 2011 6:01 pm, edited 1 time in total.

Top
 Profile  
 
 Post subject:
PostPosted: Thu Dec 08, 2011 5:58 pm 
Offline
User avatar

Joined: Mon Sep 27, 2004 2:13 pm
Posts: 1668
The TMS9918 was used in the ColecoVision and Sega SG-1000 consoles (and numerous computers including the MSX.)

Share the same timings how? All of the master clocks are based off colorburst, and 5.37 MHz turns out to be the most convenient frequency for squareish pixels on a 256 pixel wide screen.

All of the consoles mentioned have a 5.37 MHz pixel clock (or mode in the Genesis and SNES' case), but the frame timings are not similar (apart from what is necessary to drive a TV).

The actual state machine in the NES (probably) runs at 5.37 MHz, the SMS at 10.74 MHz, the Genesis at 53.69 MHz / 4 probably, the SNES at 21.48 MHz probably.

The NES PPU was perhaps inspired by the TMS9918, but it's clearly not built upon the TMS' like the SMS and Genesis were for backwards compatibility with SG-1000 games.


Top
 Profile  
 
 Post subject:
PostPosted: Thu Dec 08, 2011 8:01 pm 
Offline

Joined: Wed May 19, 2010 6:12 pm
Posts: 2789
They all fetch bg tiles during active display and fetch sprite patterns during H-blank.


Top
 Profile  
 
 Post subject:
PostPosted: Thu Dec 08, 2011 10:20 pm 
Offline

Joined: Sat Jan 23, 2010 11:41 pm
Posts: 1161
There are many off-the-shelf video controllers for non-gaming applications, from simple text or pseudographics ones like Intel 8275 and Motorola 6845 to more complex with many raster video modes, blitter, sprites, etc, like Yamaha V9990.


Top
 Profile  
 
PostPosted: Sat Dec 29, 2018 2:24 pm 
Offline

Joined: Thu Apr 19, 2018 12:19 am
Posts: 17
Quote:
They all fetch bg tiles during active display and fetch sprite patterns during H-blank.


Hi, i havent found that in the TMS9918A/TMS9928A/TMS9929A Video DisplayProcessors pdf,
in it explains only about Vblank, there are no references to Hblank, or retrace period, about Hblank is explained in the genesis software manual, it is important that the cpu sends the order to load the sprites from 68k ram mapped vdp ports to vdp vram(write nametable) in hblank because vdp is not so busy and sample them, I wonder what happened in that document that there is no reference to hblank


Top
 Profile  
 
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 6 posts ] 

All times are UTC - 7 hours


Who is online

Users browsing this forum: No registered users and 3 guests


You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Search for:
Jump to:  
Powered by phpBB® Forum Software © phpBB Group